Thread tensioning device for sewing machines



y 1956 T. MATSUBARA ETAL 2,746,409

THREAD TENSIONING DEVICE FOR SEWING MACHINES Filed Jan. 22, 1952 3 Sheets-Sheet 1 v INVENTORJ' 441:0 ama.

y 2, 1956 T. MATSUBARA ET AL 2,746,409

THREAD TENSIONING DEVICE FOR SEWING MACHINES Filed Jan. 22, 1952 3 Sheets-Sheet 2 Fig.4.

ANGLE 0F ROTATION THE MAIN SHAY-TIN DEGREES May 22, 1956 T. MATSUBARA ET AL ,7

THREAD TENSIONING DEVICE FOR SEWING MACHINES Filed Jan. 22, 1952 3 Sheets-Sheet 3 H9 Fig. 5b. Fig. 5c.

Fig. 5d.

United States Patent '0 ,z,746,409 THREAD TENSIONING nnvrcn FOR SEWING Tom Matsubara and Denzabnro Terayama, Kita ma gu Tokmflanam ssignor to T ky Juki shi i Kei ha. ok o; Japan Applicationtlanuary '22, 1952, Serial No.2675588 Claims p i rity,.apnli. alionlapan Match 2.0, 1951 2 Claims. 01. 112- 248 This invention relates to thread tensioning devices used in sewi g machines.

Ko gyo Kabu- A11 obje of th in entic i t pr v d a imple rota y the sewing thread .as is absolutely necessary in sewing 1 machines. in a sewing machine having a rotary hook, when the rotary hook reaches a position for releasing a loop of thread the thread should be quickly taken up while the needle penetrates the cloth in preparation for submitting a new loop to the rotary hook. The loosening of the thread should be comparatively slow. It is an object of the invention to provide such an action for a sewing machine which is not of the dual shaft type.

It is a further object of the invention to provide a suitable tension and release of the sewing thread by rotating two sewing thread contact members fixed at required eccentric distances and a suitable angle on a disc concentrically attached at right angles to the main shaft.

With the above and other objects in view which will become apparent from the detailed description below, a preferred form of the invention is shown in the drawings in which:

Figure 1 is a side elevational view of the head of a sewing machine;

Figure 2 is a similar view with parts removed to show the arrangement of the interior;

Figure 3 is a longitudinal cross-sectional view with parts in elevation;

Figure 4 is a diagram illustrating the motion desired;

Figures Sathrough 5 show end elevational views illustrating the relative motions of various parts during one cycle of forming a stitch;

Figure 6 is a diagram illustrating the invention.

In the various views, like parts are indicated by like reference characters.

A thread T coming from a suitable supply passes through a guide 1 and a thread tension regulator 2. The thread then passes through the take-up spring 3 to the guide 4 and then passes over the thread contact member 7 to a thread guide 9 from which it returns over the contact member 7 and passes through the guides 10 and 11 to the eye of the needle 13. A second thread contact 'member 8 is also provided between the two discs 5 and 6 which are fixed concentrically with the main shaft.

The contact member 7 is also located between the two discs 5 and 6 and the members 7 and 8 are fixed at suitable eccentric distances and at a predetermined angle between the discs 5 and 6.

The double rotation mechanism of the rotary hook as correlated with the operation of the sewing thread in the thread tensioning device and the movements of the needle and rotary hook will now be explained. The thread contact members 7 and 8 while rotating with the discs around the main shaft contact and control the sewformed. by two pins as ing thread so as to give the thread the required tension and release .actions. The threadcontact members are p shown in the r wings, and the pi s h ldih e s ch movemen a hap as will mee the requirements for the change of course to be given to the sewing thread by the needle and rotary hook.

The amount to be fed bythe thread tensioning device depends upon the relative distances and angles of the thread from the axes of thethread contact members and upon the relative positions of the axes of the thread guides 4, 9 and 10. Therefore it is necessary to determine each relative positionso as to meet the requirements of tensioning the thread as required by the ditherences in "position of the needle sp ndle and the r t y hook mechanism .of the machine.

Figure 4 represents the course variation .Ofwth sewing thread with the amount of thread sent out in the'ordinate andgthe angle of rotationof the main shaft in theab- ,scissa; Curve A represents the variation of the course of the thread as caused by the sewing thread tensioning device, vwhileqcurve B represents the amount of the sewin thread draw-min under .theneedle :plate by the needle spindle and the rotary hook. Thus, range L represents the absolutely necessary amount ofxthe sewing thread-in .each phase of the rotatiQn. Curve. ,A which is the variation given by the actual tensioning device must be as close to curve B as possible and both curves must vary in parallel with each other. The band shaped clearance T represents the amount stored by the take-up spring.

The relative motions of the various parts is shown in Figures 5a through 5 In Figure 5a the needle has risen slightly from its lowest position and the thread has been loosened a little by the tensioning device so that a loop of thread has been formed alongside the needle hole and the beak of the rotary hook is about to engage this loop of thread. This period corresponds to the phase (1) in Figure 4 and just before and after this phase the course variation of the thread has temporarily stopped.

In Figure 5b the thread which has been picked up by the rotary hook is being gradually drawn through the cloth and this period corresponds to the thread drawing phase shown at (2) in Figure 4. The variation of thread by the sewing thread tensioning device is performed by the variation in thread drawn by the rotary hook.

In Figure 5c the loop of thread drawn in by the rotary hook is about to be disengaged from the rotary hook while the sewing thread tensioning device is just about to draw up the sewing thread thus released. This period corresponds to the thread raising phase (3) in Figure 4.

In Figure 5d there is shown the period wherein the thread released from the rotary hook is being further drawn up.

Figure 52 represents the period of forming the stitch by tightening. the thread while the tension given to the thread by the tensioning device undergoes a gradual variation.

Figure 5 illustrates the period just after the tip of the needle has penetrated the cloth to form the next stitch. Here the thread must be again loosened as the needle comes down so that a new loop of thread may be formed for the action of the rotary hook.

The discs 5 and 6 rotate for from the time when the thread is picked up by the rotary hook to the time when the thread is disengaged from such hook during which the thread contact members 7 and 8 are feeding thread to the rotary hook. The discs rotate another 120 from the time when the thread is disengaged to the time when the stitch has been tightened while the thread is being drawn up by the rotation of the contact members. Also during the period from the time when the thread tightens the stitch to the time when the rotary hook draws needle sinks below the cloth:

If the contact points on the two pins which are sewing thread contactmembers of the lines of contact from the center are P and Q, if the positions of the thread guides are A and B, if OP and OQ, where O is the center of the disc, are r1 and r2, respectively, and if POQ=u and AOB=0, the conditions that must be satisfied.

ri/rz and angles a and are what have been resulted from experiments, and the desired sewing is obtained only within the scope limited in the specification. It is impossible to obtain the ideal sewing operation of the machine under the present invention outside of the limited scope. That is to say, if the angle is smaller the pick up of threads is done too early, thus cutting the threads, and, on the contrary, if the angle is larger the threads are made too loose and thus the vibration of threads result in the cutting of threads.

It is apparent from the above explanation that the course variation of the sewing thread by this rotary disc i type sewing thread tensioning device has complete characters of slow loosening and quick tensioning of thread.

What we claim is:

l. A sewing thread tensioning device in a sewing machine of the type in which a rotary hook makes two revolutions during a sewing cycle, comprising two discs concentrically attached to the main shaft of the machine, two pin-shaped sewing thread contact members fixed on said two discs, two thread guides, one on each side, set outside said discs, the angle formed by the center of rotation of said discs and the thread guides and the angle formed by said center of rotation and the two sewing thread contact members being substantially and the ratio of the distance from said center of rotation to one of the contact members to the distance from said center to the other contact memberis between 0.3 and 0.8.

2. A sewing thread tensioning device according to claim 1 wherein said contact members comprise cams fixed between said two discs, said two discs being concentrically attached to the main shaft of the machine.

References Cited in the file of this patent UNITED STATES PATENTS 415,814 Gibbs Nov. 26, 1889 1,732,206 Ringe Oct. 15, 1929 2,391,517 Rubel Dec. 25, 1945 

